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Explanation of Optical Terms

Plastic lenses Lenses made of a plastic resin material sometimes known as CR 39.

Polycarbonate lenses.. Tougher than traditional plastic lenses made of a polycarbonate material ,often used in rimless spectacles, less likely to break. Used in Safety eyewear.

 Hi index Lenses… Plastic lenses made of a denser resin enabling the lenses to be thinner and lighter than traditional plastic lenses. There are differing degrees shown by there index number, ie A standard lens has a index number of 1.52. Hi index lenses start from 1.6  1.67  1.7

 Bifocal lenses… Lenses which incorporate the distance and reading prescriptions in one lens. The top part of the lens is for distance vision the lower part for reading vision. There is a dividing line between the two. There are many different types of bifocals with different sizes and shapes of reading segments

 Multifocal Lenses…Lenses which gradually change power as you look down the lens from distance to reading. Commonly known as Varifocal lenses. There are many different lenses such as Varilux ..Progressive…Graduate.. Impressions. Each manufacture having their own names.


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